Anionic Probe Research Articles

Electrochemical characterization of carbon black in different redox probes and their application in electrochemical sensing

Carbon black - materials rich in carbon nanostructures - have been successfully applied as modifiers of electrochemical transducers, rivalling other carbon nanomaterials for cost and ease-of-use. Despite the remarkable promise of this nanomaterial, no study has yet comparatively characterised a wide range of different grades of carbon black for their utility in electrochemical sensors. Here, we explore several commonly-studied carbon black grades (N220, N234, N326, N330, N339, N375, N550, N660 and Lamp Black-101), alongside relatively newer grades (Printex®-200, Printex® G, Printex® XE-2B, and Printex® Zeta) for their application in electrochemical sensors. The effects of coating glassy carbon electrodes with carbon black on electrode performance were studied by cyclic voltammetry using three redox probes: ferri-/ferrocyanide (anionic probe molecules), ferrocenemethanol (neutral) and hexaammineruthenium (cationic). Raman Spectroscopy characterisation of the different grades associated a lower degree of graphitisation with superior electrode modifiers. Generally, modification increased the anodic peak current for ferri-/ferrocyanide probes; and lowered anodic potential for ferri-/ferrocyanide and hexaammineruthenium probes. Increases in peak current and potential observed at ferrocenemethanol are consistent with the increased tendency for this probe to adsorb to the surface of modified electrodes. N330 and Printex® XE-2B displayed the best electrocatalytic properties in terms of enhanced peak currents and lowered anodic overpotentials for the redox probes. CB grades were used to modify screen-printed carbon electrodes and the obtained sensors examined for anodic detection of reduced nicotinamide adenine dinucleotide (NADH) cofactor by cyclic voltammetry. Printex® XE-2B significantly improved the detection of NADH and was further used for chronoamperometric detection of NADH at low overpotentials. Grades N220, N375, N550 and P-G showed their suitability as enzyme scaffolds for sensor fabrication, as determined by their preservation of the activity of a NAD-dependent aldehyde dehydrogenase.

Molecular-Scale Interactions in the Choline Chloride-Ethylene Glycol Deep Eutectic Solvent System: The Importance of Chromophore Charge in Mediating Rotational Dynamics.

We report on the rotational diffusion dynamics of three chromophores (disodium fluorescein, oxazine 725, and perylene) in a series of choline chloride-ethylene glycol (ChCl:EG) deep eutectic solvent (DES) systems. We observe behavior independent of DES bulk viscosity for the cationic and neutral probes and behavior that is consistent with stick-limit interactions for the modified Debye-Stokes-Einstein model for the anionic probe. This finding indicates that the anionic species is integral to the interactions between DES constituent species that are responsible for local organization, consistent with previous MD simulations that showed higher interaction energies associated with both the hydrogen bond donor (EG) and hydrogen bond acceptor (Ch+) interactions with Cl- in ChCl:EG mixtures. The reorientation data reported here also indicate a region around 15 mol % ChCl where the stoichiometric relationship between the species gives rise to changes in the details of intermolecular interactions.

A dual channel superoxide anion probe for the rapid visualization of scrap leather-induced neuroinflammation using an intramolecular electron transfer-integrated near-infrared platform

Chemicals used in leather processing can penetrate the human skin and respiratory system, causing neuroinflammation and pose health risks. This study addresses the lack of effective treatments for this condition by focusing on the design and synthesis of a novel dual-channel fluorescence probe HMDP. HMDP, equipped with coumarin as the fluorophore, quinolinium ion as its mitochondrial localization group, and diphenylphosphinoyl as the O2•− recognition site, demonstrated significant dual-channel fluorescence amplification at 570 and 714 nm. Incorporating two non-interfering fluorescent channels enabled cross-verification, enhancing accuracy. This research systematically assessed fluctuations in O2•− levels in a cell oxidative stress model induced by scrap leather using HMDP. The results underscored the considerable potential of this mitochondrial-targeted near-infrared fluorescent probe for monitoring scrap leather-induced cell oxidative stress. This research contributes valuable insights into the neuroinflammatory effects induced by leather processing chemicals, providing a foundation for potential therapeutic interventions to mitigate health risks associated with such exposures.

Theoretical design of novel fluorophores for near-infrared fluorescent probes of peroxynitrite

On the basis of the experimentally reported near-infrared (NIR) fluorescent probe for peroxynitrite anions (ONOO–) DDAO-PN (DDAO = 1,3-dichloro-7-oxygen-9,9-dimethyl-2(9H)-acridinone, PN = 4- methylene benzeneboronic acid pinacol ester, DDAO-PN connecting 7-oxygen of DDAO with 4- methylene of PN), six DDAO derivatives DDAO-Px (x = 1–6) were designed. The fluorescence response mechanism and characteristics of the DDAO-PN probe to ONOO– were explored and the molecular structures, molecular orbital, and electron transfer during excitation and emission in DDAO-PN and DDAO-Px (x = 1–6) were comparatively analyzed in detail through the density functional theory (DFT) and time-dependent DFT calculations. The significant intramolecular charge transfer (ICT) effect in DDAO-PN were found to be released when PN (as the recognition domain of ONOO– in the recognition process) was removed, rendering DDAO-PN being an effective “off-on” NIR ONOO– fluorescent probe. The introduction of different electron-donating/accepting substituents in DDAO-Px significantly changed the electronic structures and thus the fluorescent properties, which finally modified the probe efficiency. This work clarifies the structure-property relationship in DDAO-Px type NIR probes and thus provides theoretical guidance for designing new NIR fluorescent probe.

Investigations of the relationships between structure and electrochemical properties of fullerenol nanoaggregates

Hybrid materials containing fullerenols have been used as electrodes in many applications, such as electrochemical biosensors for different targets or in hydrogen and oxygen reduction reactions. However, electrodes modified with fullerenols and without other electroactive materials are not much explored, and the electrochemical behavior of fullerenols themselves is not well-established in the literature. Herein, we report the basic electrochemical characterization of electrode modified with fullerenol and some correlations between material structure and electrochemical behavior. The prepared fullerenol is composed of nanoaggregates dispersed in an organic solvent. Although the electrode modified with pristine fullerene is slightly less active to [Fe(CN)6]3−/4− concerning bare glassy carbon electrode (GCE), the fullerenol-based electrode presents a much lower activity that is slightly increased after electrochemical reduction. The drying process greatly influences the electrochemical performance of the electrodes modified with fullerenol, and fast drying can form ruptures with micrometric dimensions that provide a particular behavior towards the anionic probe. The reduction process increases the number and sizes of these ruptures and changes the electrochemical response. Moreover, the fullerenol-based electrode is more active for [Ru(NH3)6]3+ than the bare GCE, and the activity was increased after reduction. However, the electrochemical response to the cationic probe is characteristic of macroelectrodes regardless of the drying process or reduction. This work opens new perspectives in the electrochemical studies of modified carbon nanomaterials, with the possibility of producing carbon-based electrodes selective to charged probes by controlling the carbon materials' molecular and microscale structures.

Turn-on Near-Infrared Phosphorescent Recognition of Anion Based on Self-Assembly of Cyclometalated Platinum Complexes That Induce Oncosis and Monitor Living Cells.

The design of bio-responsive functional molecular materials that can undergo self-assembly to form nanostructures within cells in response to cellular endogenous stimuli and the clarification of their prospective reaction mechanisms are of paramount significance. This work aims to elucidate the spatiotemporal generation of subcellular nanostructures and their influence on cellular functionality. Three sets of cyclometalated platinum complexes have been designed and synthesized as near-infrared phosphorescent turn-on probes for specific anions based on dynamic self-assembly in aqueous solution. The augmentation of the quantity of aromatic rings in the NN bidentate ligand of the complex modifies both the intensity of the intermolecular Pt-Pt interaction and the capacity to generate self-assembled nanowires with near-infrared emission. Besides, we explored the impact of the CN ligand's substituent effect on anion recognition, which revealed that complexes with electron-absorbing F atom substitution exhibit superior selectivity for Br-. These complexes display vivid green turn-on luminescence upon interaction with cellular biomolecules, enabling dynamic monitoring of their subcellular distribution and their interaction on diverse conditions. Furthermore, our complexes were observed to induce oncosis in cancer cells, underscoring the potential of our work in facilitating in vitro diagnosis and developing effective theranostic agents for cancer therapy.

Trivalent anions as probes of the CFTR channel pore.

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel uses positively charged amino-acid side-chains to form binding sites for permeating anions. These binding sites have been investigated experimentally using a number of anionic probes. Mutations that alter the distribution of positive and negative charges within the pore have differential effects on the binding of monovalent versus divalent anions. This study uses patch clamp recording from wild-type and pore-mutant forms of CFTR to investigate small trivalent anions (Co(NO2)63-, Co(CN)3- and IrCl63-) as potential probes of anion binding sites. These anions caused weak block of Cl- permeation in wild-type CFTR (Kd ≥ 700 μM) when applied to the intracellular side of the membrane. Mutations that increase the density of positive charge within the pore (E92Q, I344K, S1141K) increased the binding affinity of these anions 80-280-fold, and also greatly increased the voltage-dependence of block, consistent with fixed charges in the pore affecting monovalent : multivalent anion selectivity. However, high-affinity pore block by Co(NO2)63-apparently did not alter channel gating, a hallmark of high-affinity binding of divalent Pt(NO2)42- ions within the pore. This work increases the arsenal of probes available to investigate anion binding sites within Cl- channel pores.

Supramolecular assemblies of organogelators featuring benzimidazole and long‐chain pyridine dicarboxyamide

AbstractTwo organogelators, CO‐01 and CO‐03, featuring benzimidazole and long‐chain pyridine carboxyamide groups were prepared and their physical properties were fully explored. CO‐01 and CO‐03 are capable of transforming various organic solvents to organogels. The morphologic investigations of these organogels have shown that the supramolecular assemblies, in the forms of fibers and spheres, are readily generated from the aggregates of CO‐01 and CO‐03. The sol–gel interconversion can be readily achieved by tuning the gelator concentration and temperature. By manipulating the redox state of anthraquinone group in CO‐03, the gel–sol transition for the organogels of CO‐03 can be reversibly tuned by either chemical or electrochemical oxidation/reduction reactions. The presence of polarized imidazole and amide N–H groups allows anion‐induced gel collapse. The accompanying colorimetric and ratiometric fluorescent responses of gels CO‐01 and CO‐03 to F− and CN− render these organogelators being sensitive and selective anion probes.

Research Progress on Naphthalimide Fluorescent Probes

AbstractNaphthalimide derivatives are attracting increasing attention as fluorescent probes due to their excellent modifiability and photophysical properties. Their large, rigid coplanar structures and conjugated systems enable easy generation of fluorescence. The imide units and bromonaphthalene functionality offer facile and concise modification pathways in preparing amenable probes for different metal cations, anions, small molecules, and organelles. Therefore, naphthalimide probes have great potential for application in research fields, such as analytical chemistry, cell biology, and clinical diagnosis.

An innovative fluorescent probe for the detection of cyanide - enhanced sensitivity by controlling its electrostatic potential and suitable for applications such as cell imaging and food analysis

As cyanide is a huge hazard to the environment and human health, the study of the method of detecting low concentrations of cyanide is of great significance. In general, materials with strong positive electrostatic properties can use electrostatic attraction to enrich anions in the water near the materials, then realize rapid detection of low concentration anions by fluorescent probes. In this paper, fluorescent probes PI-S, PI-I and PI-N with cyanide-specific recognition and different charges were synthesized to study the relationship between the charge effect of probes and the sensing sensitivity. Through the zeta potential test and the calculation of the surface electrostatic potential, the positive electricity of PI-S, PI-I and PI-N gradually increased, the ΔG < 0 of the adsorption process gradually decreased, CN– could be aggregated to the vicinity of probes. As a result, the detection limit of the probe was gradually reduced from 1.07 × 10−6 to 5.03 × 10−8 M, the sensitivity was significantly enhanced. Therefore, this is expected to be a new strategy to improve the sensitivity of anion probes by increasing the positive electricity of molecules. In addition, PI-N has good anti-interference ability, short response time and certain application value in cell imaging and identification of endogenous cyanide in food.

Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy.

Confining water to nanosized spaces creates a unique environment that can change water's structural and dynamic properties. When ions are present in these nanoscopic spaces, the limited number of water molecules and short screening length can dramatically affect how ions are distributed compared to the homogeneous distribution assumed in bulk aqueous solution. Here, we demonstrate that the chemical shift observed in 19F NMR spectroscopy of fluoride anion, F-, probes the location of sodium ions, Na+, confined in reverse micelles prepared from AOT (sodium dioctyl sulfosuccinate) surfactants. Our measurements show that the nanoconfined environment of reverse micelles can lead to extremely high apparent ion concentrations and ionic strength, beyond the limit in bulk aqueous solutions. Most notably, the 19F NMR chemical shift trends we observe for F- in the reverse micelles indicate that the AOT sodium counterions remain at or near the interior interface between surfactant and water, thus providing the first experimental support for this hypothesis.

Transforming the fluorescent fluorine anion probe from on-off to ratiometric type by a tiny modification on the triarylborane group

Based on the electron-deficient property of the pπ orbital in boron atoms, varies of triarylborane-based materials have been designed as the fluorescent probes to detect fluorine anions. However, the strong Lewis acid/base interaction between the probes and F− anions usually quenches the fluorescence, leading to relatively low performance. In this work, two triarylborane-based fluorescent F− anion probes B1 and B2 were developed. Both were highly emissive with fluorescence quantum yields larger than 0.7 and showed impressive sensitivity and selectively to F− anions. The limit of detection (LOD) of B2 was as low as ca. 0.16 µM, which was one of the lowest LOD for F− anions. More importantly, by simply replacing a sp2 hybridized carbon atom in B1 with a sp2 hybridized nitrogen atom to from B2, the responses to F− anions were transformed from on-off to ratiometric fashion. Based on theoretical calculations, this admired transformation was assigned to the significant differences in the distribution of key molecular orbitals, the components of the S1 state and the oscillator strengths between related species.

ESIPT-based probes for cations, anions and neutral species: recent progress, multidisciplinary applications and future perspectives.

Fluorescent and colourimetric probes for small analytes (cations, anions and neutral molecules) have drawn significant attention in recent years. These probes interact with analytes and induce spectral change due to the variations in the photo-physical properties of the fluorophore/chromophore used. Among several photo-physical mechanisms, ESIPT (excited state intramolecular proton transfer) based probes are more advantageous due to their photo-physical properties viz. solvent polarity effect, large spectral shift with multi-channel fluorescence, high quantum yield etc. In recent years, ESIPT-based probes have shown several promising applications, especially monitoring small analytes in biological samples, smartphone app-assisted heavy metal detection in environmental samples, inkless writing, anti-counterfeiting applications etc. Therefore, this review is dedicated to recently reported ESIPT-based probes for small analytes. We have highlighted the organic units responsible for the ESIPT mechanism, their photo-physical parameters, selectivity and sensitivity properties and recent advances in their applications.

Exploring cationic polyelectrolyte-micelle interaction via excited-state proton transfer. Signatures of probe transfer.

Excited-state proton transfer (ESPT) is a sensitive tool for the delicate monitoring of structural reorganization, hydration level, and confinement within surfactant and polymer assemblies. Here, we investigate the interaction of a cationic polyelectrolyte, poly(diallyl dimethylammonium chloride) (PDADMAC), with micelles of differently charged surfactants using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) as an ESPT probe. We used three surfactants: anionic sodium dodecyl sulfate (SDS), cationic dodecyl trimethylammonium bromide (DTAB), and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB12), possessing the same alkyl (dodecyl) chain but varying headgroup charges. The fluorescence of HPTS residing initially within the micellar medium modulates differently in the presence of PDADMAC. For the anionic SDS and cationic DTAB micelles, the emission spectrum of HPTS does not alter significantly; however, for SB12 micelles, the emission spectrum undergoes a strong modulation upon adding the polyelectrolyte. The emission intensities quench strongly at a low concentration of PDADMAC but recover at a higher concentration. The emission intensity ratio of the two emission bands also changes significantly, implying strong modulation of the ESPT process with varying PDADMAC concentrations. The time-resolved area normalized emission spectra (TRANES) disclose single isoemissive points in the SB12 micelle at low and high concentrations of PDADMAC but two different isoemissive points (one characteristic of the SB12 micelle at 500 nm and another characteristic of the PDADMAC interface at 480 nm) in the mixed assembly at an intermediate concentration. Detailed analysis suggests that the polyelectrolyte can enforce the transfer of the anionic probe HPTS from the zwitterionic micelle to the PDADMAC assembly above a specific PDADMAC concentration. The transfer of the molecular probe between two assemblies resembles a drug sequestration event, and the study reveals necessary emission signatures.

A Novel Paper-Based Electrochemical Biosensor Based on N,O-Rich Covalent Organic Frameworks for Carbaryl Detection.

A new N,O-rich covalent organic framework (COFDHNDA-BTH) was synthesized by an amine-aldehyde condensation reaction between 2,6-dialdehyde-1,5-dihydroxynaphthalene (DHNDA) and 1,3,5-phenyltriformylhydrazine (BTH) for carbaryl detection. The free NH, OH, and C=O groups of COFDHNDA-BTH not only covalently couples with acetylcholinesterase (AChE) into the pores of COFDHNDA-BTH, but also greatly improves the catalytic activity of AChE in the constrained environment of COFDHNDA-BTH’s pore. Under the catalysis of AChE, the acetylthiocholine (ATCl) was decomposed into positively charged thiocholine (TCl), which was captured on the COFDHNDA-BTH modified electrode. The positive charges of TCl can attract anionic probe [Fe(CN)6]3−/4− on the COFDHNDA-BTH-modified electrode to show a good oxidation peak at 0.25 V (versus a saturated calomel electrode). The carbaryl detection can inhibit the activity of AChE, resulting in the decrease in the oxidation peak. Therefore, a turn-off electrochemical carbaryl biosensor based on a flexible carbon paper electrode loaded with COFDHNDA-BTH and AChE was constructed using the oxidation peak of an anionic probe [Fe(CN)6]3−/4− as the detection signal. The detection limit was 0.16 μM (S/N = 3), and the linear range was 0.48~35.0 μM. The sensor has good selectivity, repeatability, and stability, and has a good application prospect in pesticide detection.

Ionic thermoresponsive fluorescent polymers for detecting countercharged surfactants without phase separation

Thermoresponsive polymers containing ionic and fluorescent groups were designed and synthesized for use as fluorescent probes to sense ionic surfactants without phase separation. The synthesized ionic thermoresponsive fluorescent polymers interact with countercharged surfactants, resulting in increases in their fluorescence intensities, even at temperatures lower than their phase-transition temperatures. The observed increases in the fluorescence intensities are attributable to the incorporation of fluorophores within the soluble aggregates formed by the polymers and ionic surfactants at temperatures lower than the phase-transition temperatures. The synergistic effects of the hydrophobic and ionic interactions between the two moieties lead to the formation of soluble aggregates, which enhance the fluorescence of the fluorophores bound to the polymers. The fluorescence intensities of cationic and anionic fluorescent polymer probes were found to be linearly dependent on the concentrations of sodium dodecyl sulfate (SDS) and zephilamine, respectively, at the 10−5 mol/L level. Moreover, the concentration of SDS, an anionic surfactant used commonly in detergents, as determined using the cationic fluorescent probe was in keeping with that determined by the conventional methylene blue method. Thus, it was confirmed that the synthesized thermoresponsive fluorescent polymers with ionic groups can function as probes for countercharged ionic surfactants in homogeneous aqueous media without any phase-separation processes, which require hazardous organic solvents.

New Dinitrophenyl Hydrazones as Colorimetric Probes for Anions

Anion sensing is a dynamic research field due to the biological and environmental importance of some organic or inorganic anions. Hydrazones show promising properties in the design of anion chemosensors due to the presence of proton donor and acceptor sites in their structure. In this work, two novel dinitrophenyl hydrazones, functionalized with a quinoline moiety, were synthesized and characterized by spectroscopic and spectrometric techniques. The interaction between the new compounds 3a–b with different organic and inorganic anions was assessed. The two compounds showed a change in color from light yellow to magenta in the presence of H2PO4−, CH3COO−, BzO−, CN−, and F−. The interactions were analyzed by spectrophotometric titrations and the stoichiometry of the interaction was assessed by the method of continuous variation. Compound 3b showed a remarkable sensitivity to CN−, with a limit of detection of 0.35 µM. The interaction of compound 3b with CN− and F− was also analyzed by 1H NMR titrations, showing that an increasing concentration of anions induce a deprotonation of the NH and OH groups.

Assessment of the Components of the Electrostatic Potential of Proteins in Solution: Comparing Experiment and Theory.

In this work, the components of the protein electrostatic potentials in solution are analyzed with NMR paramagnetic relaxation enhancement experiments and compared with continuum solution theory, and multiscale simulations. To determine the contributions of the solution components, we analyze them at different ionic strengths from 0 to 745 mM. A theoretical approximation allows the determination of the electrostatic potential at a given proton without reference to the protein structure given the ratio of paramagnetic relaxation enhancements rates between a cationic and an anionic probe. The results derived from simulations show good agreement with experiment and simple continuum solvent theory for many of the residues. A discrepancy including a switch of sign of the electrostatic potential was observed for particular residues. By considering the components of the potential, we found the discrepancy is mainly caused by angular correlations of the probe molecules with these residues. The correction for the correlations allows a more accurate analysis of the experiments determining the electrostatic potential of proteins in solution.

Evaluation of Blood-CSF Barrier Transport by Quantitative Real Time Fluorescence Microscopy.

Transporters at the blood-cerebrospinal fluid (CSF) barrier (BCSFB) play active roles in removing drugs and toxins from the CSF. The goal of this study is to develop a fluorescence microscopy approach to quantitatively study the transepithelial transport processes at the murine BCSFB in real time. Choroid plexus (CP) tissues were isolated from mouse lateral ventricles and incubated with anionic (fluorescein-methotrexate, 8-fluorescein-cAMP) or cationic (IDT307) fluorescent probes. The CSF-to-blood transport was imaged and quantified using compartmental segmentation and digital image analysis. Real time images were captured and analyzed to obtain kinetic information and identify the rate-limiting step. The effect of transporter inhibitors was also evaluated. The transport processes of fluorescent probes can be captured and analyzed digitally. The intra- and inter- animal variability were 20.4% and 25.7%, respectively. Real time analysis showed distinct transport kinetics and rate-limiting step for anionic and cationic probes. A CP efflux index was proposed to distinguish between transepithelial flux and intracellular accumulation. Rifampin and MK571 decreased the overall transepithelial transport of anionic probes by more than 90%, indicating a possible involvement of organic anion transporting polypeptides (Oatps) and multidrug resistance-associated proteins (Mrps). A CP isolation method was described, and a quantitative fluorescence imaging approach was developed to evaluate CSF-to-blood transport in mouse CP. The method is consistent, reproducible, and capable of tracking real time transepithelial transport with temporal and spatial resolution. The approach can be used to evaluate transport mechanisms, assess tissue drug accumulation, and assay potential drug-drug interactions at the BCSFB.

A novel colorimetric and ratiometric fluorescent probe for fluoride anions based on perylene tetra-(alkoxycarbonyl) derivatives

A novel fluoride anion (F−) colorimetric and ratiometric fluorescent probe (AOP) based on perylene tetra-(alkoxycarbonyl) derivative was designed, synthesized and characterized. Probe AOP selectively detected F− with unique absorption and fluorescence changes, which were not observable for other halides and anions (Cl−, Br−, I−, AcO−, SO42−, and ClO4−). The system was studied by 1H NMR, electrochemical, and density functional to determine the properties of the interaction between AOP and F−. Planar conformation and D-A type of AOP facilitated efficient intramolecular charge transfer, resulting in red shifts of absorption/emission spectrum and ratio fluorescent response. Finally, the use of silica coated slides of the AOP to detect F− was also reported.